Cold weather conditions promote buildup of ice on vehicle surfaces. To remove the ice, large amounts of chemicals are often sprayed onto the ice to promote melting. Additionally or alternatively, electrical heating of vehicle surfaces to melt the ice involves a large energy consumption to promote sufficient deicing. The large amounts of chemicals and/or energy consumption are each a cost burden on a user of the vehicle.
Deicing is particularly challenging for airfoils, such as rotor blades, of rotorcraft vehicles, such as helicopters. State of the art deicing concepts applied to rotorcraft involve the electrothermal ice protection system. This system remains the only Federal Aviation Administration and Department of Defense approved system for rotor blade implementation.
The system comprises heaters installed in the leading edge of the blade. These de-ice heaters, around 0.0025″ thick, can be integrated in the upper spar of a blade. Furthermore, conventional materials disposed on a spar are many thousandths of an inch thick, which can hinder bondability of a material to, for example, an erosion protection layer. For deicing processes, the goal of the heaters is to quickly elevate the temperature of the ice/rotor interface above 32° F. A temperature greater than 50° F. is usually sought. The heating process only melts the interface of the ice, allowing centrifugal force inherent to the rotating blades to remove the ice from the surface. Heat applied too slowly or to thin ice formations does not liberate ice because centrifugal forces are not large enough to overcome the ice/rotor bond. The ice then locally melts and the liquid water flows to the aft portions of the blade and refreezes. This process, called runback, is disadvantageous because the refreeze location is typically outside of the area affected by the heaters and the ice cannot be removed with additional heater pulses. In addition, the refreeze location, near maximum blade thickness, is usually in a region that significantly reduces airfoil performance.
The system comprises a power generator to apply electrical energy to one or more components of the rotor blade. Depending on rotor blade structure, power densities of about 25 WSI (Watts per square inch) are required to achieve the required surface temperatures with minimum power-on times. Such power densities place a large demand on the aircraft electrical system. In order to reduce the peak power demand, the heater blankets are divided into zones. These zones are fired in a specific sequence to de-ice the blade, and this sequence can be tailored to icing conditions. However, the heaters cannot have any unheated areas between zones, which adds cost to purchasing/manufacturing these rotor blades. The heaters must form as close of a butt-joint as possible to preclude areas of the blade from being unheated and therefore not permit controlled ice release from a surface of the rotor blade. The close spacing involves precision in placement of power leads. The system includes complex control system requirements, such as sensor inputs and control sequencing. Currently, rotor blade component failures typically involve installation of one or more new blades. In some cases, rotor blade component failures render the overall blade de-ice system irreparable.
Although heater designs have been continuously improved, many rotor blade materials cannot be integrated into modern, higher strain designs because they do not possess sufficient “airworthiness” properties for harsh environments, such as mechanical strength.
Another challenge for rotor blade technology is the design of an effective and reliable deicing material that is compatible with edge erosion protection layers (such as titanium, nickel, and polyurethane) disposed on (adjacent to) a surface of a rotor blade. Erosion coatings are typically thermally insulative which necessitates large energy consumption for adequate deicing of a rotor blade surface. Thus, conventional deicing material does not possess adequate electrical properties in addition to durable erosion impact protection for longevity from harsh environments. Conventional surface coating(s) of vehicle components of an aircraft, and rotor blades in particular, are typically not highly conductive, having resistivity of hundreds of kOhms to tens of MegaOhms. Accordingly, conventional surface coatings of an aircraft can allow charge buildup on surfaces (and other components) of the aircraft. In addition to an inability to dissipate charge buildup, conventional coatings might not possess other ideal “airworthiness” properties. For example, performance as to durability parameters such as rain erosion, resistance to UV light, resistance to high temperature, resistance to low temperature, inadequate flexibility, and resistance to sand and hail damage might not be ideal for conventional surface coatings on a surface of a vehicle, such as an aircraft, exposed to harsh conditions.
What is needed in the art are materials that are both conductive and otherwise airworthy and methods of making and using the materials.